Field of the Invention
The present invention relates to a solder-mounted board on which a component is mounted by means of the solder; to a method for producing the board; and to a semiconductor device.
Background Art
Soldering is widely used for mounting, on a board, a component employed for, for example, a semiconductor device such as an LSI or WLP (wafer level package).
Such a soldering process will now be described with reference to drawings.
FIG. 6 shows the case of employing a mounting board 100 including a substrate 101; wiring layers 102 and mounting pads 103 which are provided on the substrate 101; and a solder resist 104 provided so as to cover the entire wiring layers 102 and a portion of the mounting pads 103 (FIG. 6A). A cream solder 105 is applied to the mounting board 100 (FIG. 6B), and solder bumps 106 are formed through reflowing (FIG. 6C). Subsequently, a flux 107 is applied to the mounting board 100 (FIG. 6D), and then a component 110 is applied onto the solder bumps 106 (FIG. 6E), followed by reflowing, to thereby mount the component 110 on the mounting board 100 (FIG. 6F). Thereafter, the flux is removed through washing (FIG. 6G), and an underfill 108 is charged between the mounting board and the component (FIG. 6H).
FIG. 7 shows the case where a component is mounted directly on a mounting board without use of a cream solder. A mounting board 100 similar to that described above is provided (FIG. 7A), and a flux 107 is applied thereto (FIG. 7B). A component 110 is applied to (FIG. 7C) and mounted on the board through reflowing (FIG. 7D). Subsequently, the flux is removed through washing (FIG. 7E), and an underfill 108 is charged between the mounting board and the component (FIG. 7F).
FIG. 8 shows the case where a process is simplified by employing an adhesive containing a flux (see, for example, Japanese Patent Application Laid-Open (kokai) No. H04-280443). In this case, a mounting board 100 similar to that described above is provided (FIG. 8A), and a flux-containing adhesive layer 109 is formed on the board (FIG. 8B). Subsequently, a component 110 is applied to the adhesive layer 109 (FIG. 8C) and mounted through reflowing (FIG. 8D), followed by curing of the adhesive layer 109 (FIG. 8E). In this case, charging of an underfill is omitted.
With recent high-density mounting of components on a board, in such a soldering process, the connection pitch between the components and the board is reduced, and the aforementioned SMD design may cause various problems.
For example, the process shown in FIG. 6 may cause problems in that the pitch of openings in the solder resist is reduced, and thus the cream solder provided on the board falls off, resulting in mounting failure, and in that the solder flows upward during reflowing due to a high opening aspect ratio of the solder resist 104, resulting in poor mounting reliability. In addition, this process may cause a problem in terms of variation in size of solder bumps of each pad. Meanwhile, the process shown in FIG. 7 or 8 (i.e., the process employing no cream solder) may cause a problem in that the solder of the component 110 does not reach the mounting pads 103, resulting in connection failure, which problem is associated with the relationship between the size of solder bumps of the component 110 and the opening aspect ratio of the solder resist 104.
Problems associated with recent high-density mounting of components arise not only in the mounting process, but also in the aforementioned mounting board 100 itself.
In the case of high-density mounting of components on the mounting board 100, when the size of openings in the solder resist 104 is reduced, development of the solder resist 104 may become excessive or insufficient, and problems may arise in that, for example, the solder resist 104 itself is deformed, and cracking occurs in the solder resist 104 after mounting of the component 110. When the elastic modulus of the solder resist is reduced for solving such problems (e.g., cracking), migration is likely to occur between the wiring layers 102. In the case of a substrate having wiring layers on both surfaces thereof, due to the difference in area between the wiring layers provided on the top and bottom surfaces of the substrate, the amount of the solder resist 104 applied to the top-side wiring layer may differ from that of the solder resist 104 applied to the bottom-side wiring layer, resulting in a problem in that the substrate is likely to warp through curing and shrinkage.
Also, in association with high-density mounting of components on the mounting board 100, the underfill provided for reinforcing connection portions of the component 110 mounted on the board 100 may flow outside the component 110 due to the presence of a gap between the component and the board after connection, and the amount of the resin charged below the component 110 may become insufficient (i.e., some portions may fail to be charged with the resin), resulting in poor reliability. Particularly in the case of the process shown in FIG. 8 (i.e., the process in which the underfill resin is provided in advance), since resin easily flows outside the component, the problem of shortage of the resin below the component becomes even more significant.
In order to solve such a problem, there has been proposed a flip-chip mounting board in which a wide connection pad is provided, and wiring width is reduced, so as to reliably connect the connection pad to a component (see Japanese Patent No. 3420076). Since the board according to the invention disclosed in Japanese Patent No. 3420076 has this configuration, when solder powder is melted, molten solder gathers on the wide connection pad, and intended solder bumps are formed on the surface of the connection pad, whereby a component can be reliably connected to the connection (mounting) pad.
Meanwhile, there has been proposed a technique for preventing the aforementioned charging failure of an underfill, in which the opening of an insulating film is enlarged to the outside of the outline of a mounting component, and a wiring layer is provided in an inner region of the mounting component (see Japanese Patent No. 3390664).
However, this technique cannot be applied to the case where a connection portion is present not only at the periphery of the component, but also at the center thereof.